The duckdb.reset_ddb() function should remove all temporary DuckDB tables

In #281 the function `duckdb.reset_ddb()` was added, which recreates the in memory database. This has as a sideeffect that all temporary duckdb tables are lost. We should also remove the matching Postgres tables from the catalog in that case.

This is definitely not a critical bug. The `duckdb.reset_ddb()` function is mostly meant for debugging at this point. But I at least thought we should track that this is an issue. Especially since it's probably not too hard to fix.

Start by reading the implementation of duckdb.reset_ddb() and the context from issue #281. Trace how temporary DuckDB tables are represented in the Postgres catalog. Done means resetting the in-memory database also removes the matching Postgres catalog tables.

Written by the indexing model from the issue text.